1. Field of the Invention
The present invention relates to a flat-surface fluorescent lamp, and more particularly to a flat-surface fluorescent lamp of a reflection type in which reflected light is outputted through a plane different from an anode panel.
2. Description of the Related Art
Various flat fluorescent lamps have been invented. In this kind of the fluorescent lamp, fluorescent material is excited by an electron beam. As to these flat fluorescent lamps, there are a transmission type and a reflection type. In the transmission type, such as described in Japanese Patent Laid-Open Publication No. 3-30252, a fluorescent-material layer is formed on an inner surface of an anode panel made of a transparent glass plate. From this anode panel, light radiates.
The flat fluorescent lamp of the transmission type has the anode panel whose calorific value is large. Thus, when using the transmission type as a back light of a liquid-crystal display and so forth, there arises a problem in that sometimes heat radiating from the anode panel exercises a bad influence. In order to solve this problem, Japanese Patent Laid-Open Publication No. 5-28972 discloses a fluorescent lamp in which a fluorescent-material layer and a reflection layer are formed on an anode panel to radiate the light through a cathode panel made of a transparent glass plate.
However, in the fluorescent lamp described in the above-noted Publication No. 5-28972, the light passes a line-form filament and a mesh-form grid, and then, the light radiates from the cathode panel. Due to this, line-like unevenness and mesh-like unevenness are caused in the emitted light. These sorts of unevenness are dissolved by making an outer surface of the cathode panel a ground glass. In this case, however, there arises a problem in that transmittance is lowered so that a light amount is reduced.
In view of the foregoing, it is a primary object of the present invention to provide a fluorescent lamp of a reflection type in which unevenness of light is prevented from occurring.
It is a second object of the present invention to provide a fluorescent lamp of a reflection type in which a light amount is prevented from reducing.
In order to achieve the above and other objects, the fluorescent lamp according to the present invention comprises an anode panel, a cathode panel, a filament, grid electrodes, and a light-output panel. The inside of the anode panel is formed with a reflection layer and a fluorescent layer. The cathode panel is disposed on a plane different from the anode panel. The filament is attached to the inside of the cathode panel. The grid electrodes are disposed between the filament and the anode panel. The light-output panel is made of a transparent glass plate and is disposed on another plane different from the anode panel and the cathode panel.
An electron beam emitted from the filament collides with the fluorescent layer. Upon this, the fluorescent layer is excited to emit light. The emitted light is reflected by the reflection layer to radiate from the light-output panel toward the outside of the fluorescent lamp.
In a preferred embodiment, the outside of the anode panel is provided with a heat-radiating plate. Further, the fluorescent lamp comprising the anode panel, the cathode panel and the light-output panel has a triangular-prism shape. Alternatively, the fluorescent lamp may have a polygonal section.
According to the fluorescent lamp of the present invention, the light generated by the fluorescent layer radiates from the fluorescent lamp without passing through the filament and the mesh-form grid electrode. Thus, it is possible to prevent unevenness from occurring in the light. Since the unevenness does not occur in the light, a transparent glass plate may be used as the light-output panel.
The light-output panel is provided separately from the cathode panel and the anode panel so that it is possible to efficiently cool the anode panel from the outside thereof. The fluorescent lamp has the triangular-prism shape so that mechanical strength may be improved. Meanwhile, when the fluorescent lamp has the polygonal section, it is possible to separately manufacture a cathode-panel side and an anode-panel side. Thus, manufacture efficiency may be improved.
Further, in a case that the cathode panel and the anode panel are made of a material having a coefficient of expansion which is identical with that of the light-output panel, joint portions of the respective panels are prevented from being damaged due to a mismatch of the coefficient of expansion when heating. In a case that the cathode panel and the anode panel are made of a material having lower transmittance in comparison with the light-output panel, it is possible to prevent the light from leaking through the other portions except the light-output panel.